1. Technical Field
This disclosure generally relates to an ink supplying container which stores ink by which a letter and/or an image is recorded on a recording medium by being ejected from a recording head and an image forming apparatus using the ink supplying container in which the amount of waste ink is reduced when cleaning and recovering nozzles of the recording head are executed by discharging the ink from the nozzles of the recording head by applying pressure to the ink in the ink supplying container using a pressure applying recovering method.
2. Description of the Related Art
An inkjet recording apparatus provides a recording head, a carrying belt which is rotated by a driving power transferring mechanism having a driving motor, pulleys, a driving belt, and so on, and a recording medium supplying tray. The carrying belt carries a recording medium stored in the recording medium supplying tray. A letter and/or an image is recorded on the recording medium by ejecting ink from the recording head while the recording medium is carried by the carrying belt. The inkjet recording apparatus is used in a general-use printing apparatus, a copying apparatus, a facsimile apparatus, and so on. In addition, recently, the inkjet recording system has been used to manufacture a component such as an industrial printed circuit board which needs precise processes by ejecting a solvent other than ink.
Recently, the recording speed of the inkjet recording apparatus has been high, and a large amount of recording has been executed in a short time. Therefore, the amount of ink which is consumed in the inkjet recording apparatus has been increased. In order to perform the large amount of recording, an ink tank having a large capacity is disposed at a position where a recording head is not disposed and ink stored in the ink tank is supplied to a sub tank disposed near the recording head by using an ink supplying unit such as a pump. With this, the large amount of recording can be executed.
As the recovering method of the recording head in the inkjet recording apparatus, there are a suction recovering method and pressure applying recovering method. As shown in Patent document 1, in the suction recovering method, the surface of nozzles of the recording head is covered with a cap connected to a suction pump, the pressure inside the cap is reduced by using the suction pump, and ink in the nozzles is suctioned. As shown in Patent Documents 2 and 3, in the pressure applying recovering method, pressure is applied to ink inside the recording head from an ink supplying route by using pressure pump and the ink is discharged from the nozzles.
In the suction recovering method, when the size of the recording head is large, a large cap is needed to cover the recording head; therefore, it is difficult to seal the surface of the nozzles with the cap. In addition, when the size of the recording head is large, a large reduction of the pressure is required for suctioning the ink. Therefore, it is not suitable that the suction recovering method be used in an inkjet recording apparatus which has a long-length recording head.
On the other hand, in the pressure applying recovering method, when the size of the recording head is large, a moisture retaining property is required for the cap which covers the surface of the nozzles of the recording head; however, excessive sealing performance is not required; therefore, the structure is simple. Consequently, it is preferable that the pressure applying recovering method be used in the inkjet recording apparatus using the long-length recording head.
In addition, in the inkjet recording apparatus, when printing is executed, in the recording head, the ink must not overflow from the nozzles. That is, the ink must be supplied to the recording head in a condition where the recording head is has a negative internal pressure so that a meniscus can be stably maintained. When the pressure applying recovering method is used, after discharging ink from the nozzles by changing the internal pressure in the recording head from a negative pressure to a positive pressure by using a pressure applying unit, the internal pressure in the recording head must be returned from the positive pressure to the negative pressure, which is optimal to execute printing, so as to execute again the printing every time after the recovering operations. In this, “positive pressure” signifies that the internal pressure in the ink supplying route is higher than atmospheric pressure, and “negative pressure” signifies that the internal pressure in the ink supplying route is lower than the atmospheric pressure.
As a method to give the recording head a negative internal pressure, there are a method of utilizing a water head by causing the height of the ink tank having a large capacity to be variable, and a method of utilizing the change of the volume of a sub tank. In the method of utilizing the change of the volume of the sub tank, since the height of the ink tank is not changed, the printing is stably executed and layout designing of the inkjet recording apparatus is not restrained. When the internal pressure of the recording head is made negative by utilizing the change of the volume of the sub tank, the internal pressure of the sub tank and the internal pressure of the recording head must be returned to an optimal negative pressure so that the printing can be executed again every time after recovering operations (restoring the nozzles to normal performance) of the nozzles of the recording head, that is, after changing the internal pressure of the sub tank from the negative pressure to the positive pressure.
FIG. 12 is a diagram showing a print head unit of an inkjet recording apparatus according to Patent Document 2. As shown in FIG. 12, in the print head unit, a sub tank 51 whose capacity is variable and a retractable stopper 52 which controls the expansion of the sub tank 51 are included in a container 53. The sub tank 51 is expanded by supplying ink to the sub tank 51 from an ink tank 50 while the pressure inside the container 53 is reduced by a pump 54, and the expanded sub tank 51 is stopped by the stopper 52. Then, the recovering operations are applied to a recording head 55. Therefore, after discharging ink in the sub tank 51 from the nozzles of the recording head 55 by making the pressure inside the sub tank 51 high, the pressure inside the sub tank 51 is made negative by moving the sub tank 51 away from the stopper 52 by causing the internal pressure of the sub tank 51 to be small.
In an inkjet recording apparatus in Patent Document 3, a sub tank whose capacity is variable is disposed. When recovering operations of nozzles of a recording head are executed, ink is supplied to the sub tank and the ink in the sub tank is discharged from nozzles of the recording head at a certain pressure. A part of the ink in the sub tank is discharged to the outside by stopping the supply of the ink to the sub tank and making the pressure inside the sub tank a negative pressure by causing the volume in the sub tank to be small.
[Patent Document 1] Japanese Patent No. 3581675
[Patent Document 2] Japanese Laid-Open Patent Application No. 2002-370374
[Patent Document 3] Japanese Laid-Open Patent Application No. 2001-162834
However, in the above pressure applying recovering method, every time at the recovering operations of the nozzles of the recording head, the change of the volume of the sub tank is utilized, that is, the internal pressure of the sub tank and the internal pressure of the recording head are changed from the negative pressure to the positive pressure and the pressure is returned to an optimal negative pressure which is suitable for printing. Consequently, the volume of ink corresponding to a difference between the volume of the sub tank when the internal pressure of the sub tank becomes maximum and that when the internal pressure of the sub tank becomes a negative pressure suitable for printing is forced to be discharged. Therefore, every time at the recovering operations, the amount of the waste ink becomes large. Especially, in an inkjet recording apparatus using a long-length recording head, the amount of the waste ink becomes remarkably large, and the ink cannot be effectively used.